This invention relates to a semiconductor fabrication technology and, more particularly, to a process of packaging a semiconductor chip in synthetic resin and a molding die used therein.
Conventionally, when an integrated circuit is fabricated on small areas on a semiconductor wafer, the semiconductor wafer is separated into bare chips, and the bare chip is mounted on a lead frame. The lead frame is placed in a cavity of a mold, and synthetic resin is injected into the cavity so as to seal the bare chip on the lead frame in the synthetic resin.
If granular synthetic resin is used for the packaging, the process traces the sequence shown in FIGS. 1A to 1E. Firstly, the prior art molding apparatus is described hereinbelow.
The prior art molding apparatus largely comprises a molding die 1 and an injection unit 2. The molding die 1 is split into an upper half 3 and a lower half 4, and cavities 5 and 6 are formed in the upper half 3 and the lower half 4, respectively. A pot 7 is inserted into the lower half 4, and is connected through runners 8 to the cavity 6. Ejector pins 9 are slidably inserted into holes formed in the lower half 4, and knock out plates 10 are attached to the ejector pins 9.
On the other hand, the injection unit 2 has an injection cylinder 11 fixed to an injection base plate 12 and a plunger 13 movable with respect to the cylinder 12. Namely, the plunger 13 has one end portion slidably inserted into the cylinder 11 and the other end portion slidably inserted into the pot 7. Though not shown in the drawings, a hydro-pressurizing system is connected to the cylinder 11, and supplies pressurized oil to the cylinder 11 so as to reciprocally move the plunger 13. Knock out rods 14 are upright from the injection base plate 12, and the injection base plate 12 is movable toward the lower half 4.
The prior art packaging process starts with separation of the molding die 1. The lower half 4 is spaced from the upper half 3. Bare semiconductor chips SC are mounted on a lead frame LF, and the lead frame LF is placed on the lower half 4. Although the pressurized oil maintains the plunger 13 at the upper limit, the injection cylinder 11 and the injection base plate 12 stay at a lower limit or a loading position, and the plunger 13 defines a space in the pot 7. Granular synthetic resin SR is inserted into the pot 7 as shown in FIG. 1A, and the loading work for the granular synthetic resin SR is indicated by point a in FIG. 2.
Subsequently, the lower half 4 starts toward a closed position at point b (see FIG. 2), and is brought into contact with the upper half 3 at point c (see FIG. 2). Thus, the molding die 1 is closed, and the bare semiconductor chips SC are accommodated in the cavities 5 as shown in FIG. 1B.
The granular synthetic resin SR is heated in the pot 7, and is melted. Thereafter, the cylinder 11 and the injection base plate 12 start toward an injecting position at point f (see FIG. 2), and the plunger 13 is also lifted without changing the relative position. The cylinder 11 and the injection base plate 12 reach the injecting position at point g (see FIG. 2). and the plunger 13 evacuates the molten resin from the pot 7 through runners 8 into the cavities 5/6. Thus, the molten resin is injected from point f to point g, and fills the cavities 5/6.
The molding die 1 is cooled, and the molten resin is solidified until point h (see FIG. 2), and the bare semiconductor chips SC are sealed in a synthetic resin package as shown in FIG. 1C.
Subsequently, the lower half starts toward the open position at point d (see FIG. 2), and reaches the open position at point e (see FIG. 2). The injection cylinder 11 and the plunger 13 start from the injecting position and the upper limit at point h (see FIG. 2). The injection cylinder 11 and the injection base plate 12 stop at an intermediate position at point i (see FIG. 2). However, the plunger 13 reaches the limit. As a result, the plunger 13 is spaced front the synthetic resin package PKG at point j as shown in FIG. 1D.
The injection base 12 starts toward the injecting position together with the injection cylinder 11, and the knock out rods 14 are brought into contact with the knock out plates 10 on the way toward the injecting position. The plunger 13 is lifted together with the injection cylinder 11, and the plunger 13 is brought into contact with the synthetic resin package PKG also on the way toward the injection position as shown in FIG. 1E. The injection base plate 12, the injection cylinder 11 and the plunger 13 are further moved upwardly by 1-2 millimeters, and separate the synthetic resin package PKG from the lower half 4 at point k (see FIG. 2). Thus, the synthetic resin package PKG is separated from the lower half 4, and is taken out from the molding die 1. If the plunger 13 is maintained at the upper limit, the plunger 13 is brought into contact with the synthetic resin package PKG earlier than the ejector pins 9, and the plunger would break the synthetic resin during the upward motion of the injection base plate 12.
The injection base plate 12 and the injection cylinder 11 are moved to the loading position, and the plunger 13 is moved to the upper limit. Then, the injection apparatus returns to the initial state at point m (see FIG. 2).
The granular synthetic resin SR is easily loaded into the pot 7 rather than synthetic resin tablets, and the manufacturer exactly regulates the amount of synthetic resin to be required. However, the granular synthetic resin SR carries air into the pot 7, and a void is liable to take place in the synthetic resin package PKG due to the air. The quantily of defective products due to the void are ten times larger than those produced from the synthetic resin tablets.
Japanese Patent Publication of Unexamined Application No. 4-164337 proposes to form the granular synthetic resin into synthetic resin tablets before the supply to the molding die. In detail, granular Synthetic resin is supplied to a cylinder, and is heated and pressed in the cylinder. The molten synthetic resin is shaped into tablets, and the tablet is supplied into the pot of a molding die. While the granular synthetic resin is begins heated and pressed, the air is eliminated from therefrom, and the molded synthetic resin is prevented from containing a void.
However, the granular synthetic resin is firstly changed to the synthetic resin tablets, and the synthetic resin tablets are used for the molding. Thus, the prior art packaging process is complicated. This is the first problem inherent in the prior art packaging process.
Another problem of the prior art molding process disclosed in the Japanese Patent Publication of Unexamined Application is the complicated molding apparatus. The granular synthetic resin is firstly changed to the synthetic resin tablets, and, thereafter, the synthetic resin tablets are used for the molding. In order to change the granular synthetic resin to the synthetic resin tablets, the molding apparatus requires the forming cylinder and the preheating unit for the change from the granular synthetic resin to the synthetic resin tablets. Moreover, various kinds of semiconductor device requires the synthetic resin tablets different in size, and the synthetic resin tablets different in size require different forming cylinders. Therefore, the forming cylinder is changed depending upon the semiconductor device to be molded, and the exchanging work consumes a large amount of time and labor. Thus, the second problem is the requirement of the complicated molding apparatus.
It is therefore an important object of the present invention to provide a process for packaging a semiconductor chip in synthetic resin which is simple without a complicated molding apparatus.
To accomplish the object, the present invention proposes to evacuate the air from soft synthetic resin by applying pressure thereto.
In accordance with one aspect of the present invention, there is provided a process for packaging a product in synthetic resin, comprising the steps of: a) accommodating a product and granular synthetic resin in a molding die; b) softening the granular synthetic resin so as to produce soft synthetic resin; c) applying pressure to the soft synthetic resin so as to evacuate the air from the soft synthetic resin and d) spreading the soft synthetic resin over an inside space of the molding die so as to seal the product in a synthetic resin package.
In accordance with another aspect of the present invention, there is provided a molding apparatus comprising a molding die formed with cavities for accommodating a product and runners connected to the cavities, a pot connected to the runners and accommodating granular synthetic resin, a heating means associated with the pot for heating the granular synthetic resin so as to produce soft granular synthetic resin, a pressurizing means associated with the pot and applying pressure to the soft synthetic resin so as to evacuate the air from the soft synthetic resin, and an injecting means associated with the pot and injecting the soft synthetic resin through the runners into the cavities after the evacuation of the air.